1. Field of the Invention
Embodiments of the invention provide techniques for analyzing a sequence of video frames. More particularly, to analyzing and learning behavior based on streaming video data while filtering out automatic gain control effects.
2. Description of the Related Art
Some currently available video surveillance systems provide simple object recognition capabilities. For example, a video surveillance system may be configured to classify a group of pixels (referred to as a “blob”) in a given frame as being a particular object (e.g., a person or vehicle). Once identified, a “blob” may be tracked from frame-to-frame in order to follow the “blob” moving through the scene over time, e.g., a person walking across the field of vision of a video surveillance camera. Further, such systems may be configured to determine when an object has engaged in certain predefined behaviors. For example, the system may include definitions used to recognize the occurrence of a number of pre-defined events, e.g., the system may evaluate the appearance of an object classified as depicting a car (a vehicle-appear event) coming to a stop over a number of frames (a vehicle-stop event).
Automatic gain control (also referred to herein as “autogain”) is an adaptive system for adjusting gain based on the magnitude of input, and is often used in electronic cameras to improve the dynamic range of certain images (e.g., images captured in low-lighting conditions). While the images with improved dynamic ranges may look better to human observers, such images may negatively affect a video analysis system. For example, amplification of pixel intensity and/or color drifts may affect the video analysis system's ability to correctly distinguish between pixels of an image associated with foreground objects and background pixels of the image.
In some convention video analysis systems, the autogain feature is simply turned off. Other video analysis systems attempt to correct for autogain by, for example, maintaining color constancy or modeling a specific camera's response during autogain and compensating for the response. These solutions tend to only work for specific cameras (or camera types) and scenes.